[AArch64] Add invalid 1 x vscale costs for reductions and reduction-operations. (#102105)

The code-generator is currently not able to handle scalable vectors of
<vscale x 1 x eltty>. The usual "fix" for this until it is supported is
to mark the costs of loads/stores with an invalid cost, preventing the
vectorizer from vectorizing at those factors. But on rare occasions
loops do not contain load/stores, only reductions.

So whilst this is still unsupported return an invalid cost to avoid
selecting vscale x 1 VFs. The cost of a reduction is not currently used
by the vectorizer so this adds the cost to the add/mul/and/or/xor or
min/max that should feed the reduction. It includes reduction costs
too, for completeness. This change will be removed when code-generation
for these types is sufficiently reliable.

Fixes #99760

Author: davemgreen

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -541,7 +541,15 @@ static InstructionCost getHistogramCost(const IntrinsicCostAttributes &ICA) {
 InstructionCost
 AArch64TTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
                                       TTI::TargetCostKind CostKind) {
+  // The code-generator is currently not able to handle scalable vectors
+  // of <vscale x 1 x eltty> yet, so return an invalid cost to avoid selecting
+  // it. This change will be removed when code-generation for these types is
+  // sufficiently reliable.
   auto *RetTy = ICA.getReturnType();
+  if (auto *VTy = dyn_cast<ScalableVectorType>(RetTy))
+    if (VTy->getElementCount() == ElementCount::getScalable(1))
+      return InstructionCost::getInvalid();
+
   switch (ICA.getID()) {
   case Intrinsic::experimental_vector_histogram_add:
     if (!ST->hasSVE2())
@@ -3070,6 +3078,14 @@ InstructionCost AArch64TTIImpl::getArithmeticInstrCost(
     ArrayRef<const Value *> Args,
     const Instruction *CxtI) {
 
+  // The code-generator is currently not able to handle scalable vectors
+  // of <vscale x 1 x eltty> yet, so return an invalid cost to avoid selecting
+  // it. This change will be removed when code-generation for these types is
+  // sufficiently reliable.
+  if (auto *VTy = dyn_cast<ScalableVectorType>(Ty))
+    if (VTy->getElementCount() == ElementCount::getScalable(1))
+      return InstructionCost::getInvalid();
+
   // TODO: Handle more cost kinds.
   if (CostKind != TTI::TCK_RecipThroughput)
     return BaseT::getArithmeticInstrCost(Opcode, Ty, CostKind, Op1Info,
@@ -3844,6 +3860,14 @@ InstructionCost
 AArch64TTIImpl::getMinMaxReductionCost(Intrinsic::ID IID, VectorType *Ty,
                                        FastMathFlags FMF,
                                        TTI::TargetCostKind CostKind) {
+  // The code-generator is currently not able to handle scalable vectors
+  // of <vscale x 1 x eltty> yet, so return an invalid cost to avoid selecting
+  // it. This change will be removed when code-generation for these types is
+  // sufficiently reliable.
+  if (auto *VTy = dyn_cast<ScalableVectorType>(Ty))
+    if (VTy->getElementCount() == ElementCount::getScalable(1))
+      return InstructionCost::getInvalid();
+
   std::pair<InstructionCost, MVT> LT = getTypeLegalizationCost(Ty);
 
   if (LT.second.getScalarType() == MVT::f16 && !ST->hasFullFP16())
@@ -3888,6 +3912,14 @@ InstructionCost
 AArch64TTIImpl::getArithmeticReductionCost(unsigned Opcode, VectorType *ValTy,
                                            std::optional<FastMathFlags> FMF,
                                            TTI::TargetCostKind CostKind) {
+  // The code-generator is currently not able to handle scalable vectors
+  // of <vscale x 1 x eltty> yet, so return an invalid cost to avoid selecting
+  // it. This change will be removed when code-generation for these types is
+  // sufficiently reliable.
+  if (auto *VTy = dyn_cast<ScalableVectorType>(ValTy))
+    if (VTy->getElementCount() == ElementCount::getScalable(1))
+      return InstructionCost::getInvalid();
+
   if (TTI::requiresOrderedReduction(FMF)) {
     if (auto *FixedVTy = dyn_cast<FixedVectorType>(ValTy)) {
       InstructionCost BaseCost =

llvm/test/Analysis/CostModel/AArch64/arith-fp-sve.ll

@@ -8,6 +8,7 @@ define void @fadd() {
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V4F16 = fadd <vscale x 4 x half> undef, undef
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V8F16 = fadd <vscale x 8 x half> undef, undef
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V16F16 = fadd <vscale x 16 x half> undef, undef
+; CHECK-NEXT:  Cost Model: Invalid cost for instruction: %V1F32 = fadd <vscale x 1 x float> undef, undef
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V2F32 = fadd <vscale x 2 x float> undef, undef
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V4F32 = fadd <vscale x 4 x float> undef, undef
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V8F32 = fadd <vscale x 8 x float> undef, undef
@@ -19,6 +20,7 @@ define void @fadd() {
   %V8F16 = fadd <vscale x 8 x half> undef, undef
   %V16F16 = fadd <vscale x 16 x half> undef, undef
 
+  %V1F32 = fadd <vscale x 1 x float> undef, undef
   %V2F32 = fadd <vscale x 2 x float> undef, undef
   %V4F32 = fadd <vscale x 4 x float> undef, undef
   %V8F32 = fadd <vscale x 8 x float> undef, undef
@@ -34,6 +36,7 @@ define void @fsub() {
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V4F16 = fsub <vscale x 4 x half> undef, undef
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V8F16 = fsub <vscale x 8 x half> undef, undef
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V16F16 = fsub <vscale x 16 x half> undef, undef
+; CHECK-NEXT:  Cost Model: Invalid cost for instruction: %V1F32 = fsub <vscale x 1 x float> undef, undef
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V2F32 = fsub <vscale x 2 x float> undef, undef
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %V4F32 = fsub <vscale x 4 x float> undef, undef
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %V8F32 = fsub <vscale x 8 x float> undef, undef
@@ -45,6 +48,7 @@ define void @fsub() {
   %V8F16 = fsub <vscale x 8 x half> undef, undef
   %V16F16 = fsub <vscale x 16 x half> undef, undef
 
+  %V1F32 = fsub <vscale x 1 x float> undef, undef
   %V2F32 = fsub <vscale x 2 x float> undef, undef
   %V4F32 = fsub <vscale x 4 x float> undef, undef
   %V8F32 = fsub <vscale x 8 x float> undef, undef

llvm/test/Analysis/CostModel/AArch64/cttz_elts.ll

@@ -3,6 +3,7 @@
 
 define void @foo_no_vscale_range() {
 ; CHECK-LABEL: 'foo_no_vscale_range'
+; CHECK-NEXT:  Cost Model: Invalid cost for instruction: %res.i64.nxv1i1.zip = call i64 @llvm.experimental.cttz.elts.i64.nxv1i1(<vscale x 1 x i1> undef, i1 true)
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %res.i64.nxv2i1.zip = call i64 @llvm.experimental.cttz.elts.i64.nxv2i1(<vscale x 2 x i1> undef, i1 true)
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %res.i64.nxv4i1.zip = call i64 @llvm.experimental.cttz.elts.i64.nxv4i1(<vscale x 4 x i1> undef, i1 true)
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %res.i64.nxv8i1.zip = call i64 @llvm.experimental.cttz.elts.i64.nxv8i1(<vscale x 8 x i1> undef, i1 true)
@@ -45,6 +46,7 @@ define void @foo_no_vscale_range() {
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 12 for instruction: %res.i32.v32i1.nzip = call i32 @llvm.experimental.cttz.elts.i32.v32i1(<32 x i1> undef, i1 false)
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;
+  %res.i64.nxv1i1.zip = call i64 @llvm.experimental.cttz.elts.i64.nxv1i1(<vscale x 1 x i1> undef, i1 true)
   %res.i64.nxv2i1.zip = call i64 @llvm.experimental.cttz.elts.i64.nxv2i1(<vscale x 2 x i1> undef, i1 true)
   %res.i64.nxv4i1.zip = call i64 @llvm.experimental.cttz.elts.i64.nxv4i1(<vscale x 4 x i1> undef, i1 true)
   %res.i64.nxv8i1.zip = call i64 @llvm.experimental.cttz.elts.i64.nxv8i1(<vscale x 8 x i1> undef, i1 true)

llvm/test/Analysis/CostModel/AArch64/sve-arith.ll

@@ -43,13 +43,34 @@ define void @scalable_mul() #0 {
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %mul_nxv8i16 = mul <vscale x 8 x i16> undef, undef
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %mul_nxv4i32 = mul <vscale x 4 x i32> undef, undef
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %mul_nxv2i64 = mul <vscale x 2 x i64> undef, undef
+; CHECK-NEXT:  Cost Model: Invalid cost for instruction: %mul_nxv1i64 = mul <vscale x 1 x i64> undef, undef
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;
 entry:
   %mul_nxv16i8 = mul <vscale x 16 x i8> undef, undef
   %mul_nxv8i16 = mul <vscale x 8 x i16> undef, undef
   %mul_nxv4i32 = mul <vscale x 4 x i32> undef, undef
   %mul_nxv2i64 = mul <vscale x 2 x i64> undef, undef
+  %mul_nxv1i64 = mul <vscale x 1 x i64> undef, undef
+
+  ret void
+}
+
+define void @scalable_add() #0 {
+; CHECK-LABEL: 'scalable_add'
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %add_nxv16i8 = add <vscale x 16 x i8> undef, undef
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %add_nxv8i16 = add <vscale x 8 x i16> undef, undef
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %add_nxv4i32 = add <vscale x 4 x i32> undef, undef
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %add_nxv2i64 = add <vscale x 2 x i64> undef, undef
+; CHECK-NEXT:  Cost Model: Invalid cost for instruction: %add_nxv1i64 = add <vscale x 1 x i64> undef, undef
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
+;
+entry:
+  %add_nxv16i8 = add <vscale x 16 x i8> undef, undef
+  %add_nxv8i16 = add <vscale x 8 x i16> undef, undef
+  %add_nxv4i32 = add <vscale x 4 x i32> undef, undef
+  %add_nxv2i64 = add <vscale x 2 x i64> undef, undef
+  %add_nxv1i64 = add <vscale x 1 x i64> undef, undef
 
   ret void
 }